3-D motion pictures are generally produced by simultaneously photographing a subject using two motion picture cameras positioned to provide "left eye" and "right eye" views of the subject. The images recorded on films in those cameras are then simultaneously projected onto a screen and are optically coded in some way so that the left eye of the viewer sees only the images that were recorded by the "left eye" camera while the viewer's right eye sees only the "right eye" images. The viewer then perceives a stereoscopic or 3-D effect.
In the presentation of 3-D motion pictures, it is important that the two sets of images projected onto the screen are in proper alignment to avoid viewer eyestrain. Human eyes naturally move in unison. If the images are not projected in alignment, the viewer's left eye will attempt to follow the left eye images while the right eye will attempt to follow the right eye images. For example, image misalignments may result in the viewer trying to "cross" eyes vertically or diverge eyes ("walleye"). These unnatural eye movements result in muscle strain that may lead to discomfort or headaches.
It has been observed that proper image alignment is of particular importance when 3-D images are projected onto a dome-shaped screen.
Projected image misalignments can occur as a result of camera misalignment when the original films were made and due to errors and tolerance problems in making prints from the original films. The misalignments are partly random, but are often systematic, i.e. are likely to be reasonably constant during any individual scene in a film. Due to their partly random character, such misalignments cannot be compensated for by appropriate setting up of the projectors when the motion picture is presented.
An object of the present invention is to provide a method and an apparatus for correcting projected image misalignments.